Lube Tip: How Oxidation Changes Oil

Once the oxidation process occurs, five major changes in the oil result in the following:

Colour becomes darker – changes from transparent or translucent in colour to some degree of discoloration toward the point of complete opacity.

Odour becomes pungent and acetic due to the presence of excessive organic petroleum acid and similar products of oxidation.

Acidity increases – changes from a neutralisation number from 0.06 to 0.12 KOH mg/g to well above 2.0 can occur.

Viscosity increases – the viscosity of an oil frequently may double or triple due to oxidation. Oxidative thickening is capable of producing fluids that have the consistency of molasses-like sludge under high operating temperature conditions.

Insolubles precipitate (sludging occurs) – after an induction period, the deterioration of an oil gradually accelerates until the formation of organic acids of deposition of sludge completely destroys the oil.